Motor starting and control mechanism



June 2, 1931. H, A H 1,807,997

4 MOTOR STARTING AND CONTROL MECHANISM Filed NOV. 7, 1928 J2 15- .JE'

Patented June 2, 1931 HAROLD .A. MAXFIELD, F WORCESTER, MASSACHUSETTS MOTOR STARTING AND CONTROL MECHANISM Application filed November 7, 1928.

This invention relates to starting and control mechanism for direct current motors, particularly where such motors are frequently started and stopped under heavy load 6 conditions. g

It is the object of my invention to simplify the control mechanism, to reduce the current and heat losses and to secure greater service from agiven size of motor.

With this general object in View, my invention relates in part to the provision of an improved and novel current control device in a direct current motor.

In the preferred form, an inductive resistance is placed in parallel with the non-inductive resistance heretofore commonly used.

y invention further relates to arrangements and combinations of parts which will be hereinafter described and more particularly pointed out in the appended claims.

Preferred applications of my invention are shown in the drawings in which Fig. 1 is a diagrammatic View showing my improvements applied to a direct current series motor;

Fig. 2 is atime-current chart, illustrating the operation of my invention;

Fig. 3 shows my improvements applied to a shunt type of direct current motor;

Fig. 4 is a diagrammatic view indicating aslight modification; and

Fig. 5 is adiagrammatic View ofa further modification.

Referring to Fig. l, I have shown a seriestype, direct current motor having an armature A, a series field coil F, a starting resistance R, a so-called plugging resistance R, and a main switch or contactor 10, these parts being'of a more or less usual consruction.

I have also provided an inductive resistance 12, mounted in series with an additional non-inductive resistance 13, these resistances 12 and 13 being mounted in parallel with the starting resistance R previously described. The inductive resistance 12 may have either an air core or an iron core.

The contactor 14 is provided for short-circuiting the resistance R, and a contactor 15 Serial No. 317,803.

for short-circuiting the parallel resistances 12 and 13.

The resistance R m ay be omitted if the motor is not to be reversed or if it is to be reversed by means other than that commonly 4 77 termed plugging The operation of m y improved star-ting mechanism is as follows, reference being made to Fig. 2

It is assumed that the switches or contactors 14 and 15 are ope switch 10 is closed att n and that the main he point 20, immedi ately followed by the closing of the contactor 14 at the point 21, which resistance R. closed, the current will cated by the point 22,

starting torque of rotation is a flow of current armature A is cuts out the plugging As soon as the switch 14 is rise to the value indiat which point the by the parallel In the circuit through the resistances 12 and 13 very little current flows at this time because of the transient inductive circuit, tion to the flow 0f field of the inductive creasing.

current action of this presenting great obstruccurrent while the magnetic resistance 12 is in- 'As the armature picks up speed, a counter electro-motive force is developed which gradually reduces the current value to the point r 23 to Fig. 2. During this gradual lowering of the. current value, however, the inductive resistance 12 becomes more magnetic energy obstruction to the of gradually cutting i flow creasing amount of current fully stored with and presents less and less of current.

e resistance 12 therefore has the effect tself out and an inis allowed to flow through the resistances 12 and 13. This modifies the reduction 1n current flow, as indicated in Fig. 2, and causes be spaced at a greater tune the point 21.

the point 23 to interval from When the current finally dropsto the value indicated at 23, an automatic device closes the switch 15, cutting and 12 and 13 entirely immediately increases,

out the resistances R and the current flow as indicated at the point 24;. As the motor thereafter picks up more speed, the current falls according to the normal characteristic of the motor, as indi cated by the curve 25.

A common form of automatic device for closing the switch 15 is indicated in Fig. 1 and comprises a solenoid plunger 30 for the switch 15,a solenoid plunger 32 pivotally 16 connected to a lever 33 and supporting a weight IV and also a plurality of solenoid coils A, B and G. When the motor is at rest the coils A, B and C are deenergized and the weight W holds the switch 15 open. As the motor starts up, the current through the coil A increases to a point where the weight W is lifted anc the lever 33 swings downward away from the plunger 30. By this time, however, the solenoid coil B is energized sufficiently to hold the plunger 30 raised and the switch 15 opened. IV hen the current drops, however, to the point 23 (Fig. 2) the weight of the plunger 30 overcomes the coil Band the switch 15 closes. As soon as the switch closes the coil 0 is energized and this coil is arranged to act in the opposite direction from the coil B and to thereafter hold the switch 15 closed even when the current in the coil B increases as indicated at 24. I

This automatic device is of the usual construction and the details thereof form no part of my present invention.

In Fig. 1 I have indicated a certain amount of non-inductive resistance 13 in series with the inductive resistance '12, but under certain conditions the shunt or parallel resistance may be entirely inductive, as indicated at 30 in Fig. 4;. V

. For a compound motor, the operation will be substantially the same as for a series m0- ;tor, a shunt coil 32 being connected as indicated in Fig. 1 entirely around the armature, the series field, and the control mechanism above described.

The arrangement for a shunt motor is indicated in Fig. 3, with the shunt coil 10 connected around the armature and starting mechanism, and with the control mechanism inserted in series with the brushes.

In'Fig. 5, I have shown an inductive resistance 31 in series with. the motor, which is of "value in producing a slow-starting or cushion effect, when used in combination with my control mechanism involving the resistances R, 12 and 13. The resistance B may be either used or omitted in this combination.

Having described the construction and operation of my improved starting and control mechanism, I will further explain the advantages thereof.

In the first place, the single switch or contactor 15 takes the place of two or more similar switches which have been heretofore found necessary until my inductive resistance 12 was used, it being necessary to cut out the resistance R in sections, reducing the resistance as soon as the current dropped to a predetermined level, which occurred much more promptly when a simple non-inductive resistance was used.

With my improved construction, the inductive resistance 12 acts in effect to cut itself out as it becomes stored with energy, thus reducing the number of automatic cutouts to a minimum. Furthermore, it will be noted that the; inductive resistance 12 economizes current, as it acts to store up energy and feed it back into'the system rather than converting the electricity into the form of heat which passes out of the system, as is the case with the usual non-inductive resistance.

be secured by proper design so that the same starting perform'ance'of the motor may obtained with less loss in the motor. This end may be gained by decreasing the value of .The action of thisnew control device may current at 22 and 24 (Fig. 2) and increasing 7 the value of current at 23. This reduces the temperature rise in the motor and it is frequently found that asmaller size motor will" perform the same duty without over-heating that required a larger motor under the old control methods, unless a large number of automatic cut-out devices are employed, which scheme is prohibitive in cost and impractical beyond a certain point.

If it is particularly desired to speed up the operation of the motor rather than to reduce the size, aresistance may be so designed that the point 23will be reached more promptly and the starting period will be reduced, this operation being commonly accomplished,

however by a greater heat loss.

Having thus'described my invention and the advantages thereof, I do not wish to be limited to the details herein disclosed otherwise than as set forth in the claims, but what I claim is 1. A direct current circuit comprising a motor having'an armature, a non-inductive resistance in series therewith, an inductive resistance in series with said armature but in parallel with said non-inductive resistance, and means to short circuit said parallel resistance on the occurrence of a predetermined drop in armature current.-

2. A direct current circuit comprising a motor having an armature, a field coil in series therewith, a non-inductive resistance in series with said'armature and said entire field coil, and an inductiveresistance also in series w1th saldarmature and said entire field coil but in parallel with said n0n-inductive reslstance.

3. A direct current circuit comprising a motorhaving an armature, a non-inductive resistance in series therewith, and aninductive, resistance and a non-inductive resistance in series with each other and collective-- Lil ly in parallel to said first-mentioned resistances.

4. A direct current circuit comprising a motor having an armature, a non-inductive resistance in series therewith, an inductive resistance and a non-inductive resistance in series with each other and collectively in parallel to said first-mentioned resistance, and means to short-circuit said parallel resistances.

In testimony whereof I have hereunto affixed my signature.

HAROLD A. MAXFIELD. 

